Adam Optimizer implementation

[sixilli]

This is my first pull request ever so hopefully it's not too far off from usable. I'm having some difficulties with testing my code. I plugged in my adam optimizer to the example and the trained network guessed 0.0 four times. While the default code within the example folder for a MLP worked as planned.

For the overall structuring of the code I did my best to follow the RMSPROP optimizer.

EDIT: Fixed some math errors and it seems to operate as expected now. Both the cost is decreasing and it correctly passed the example test. I also improved the memory usage of the previous version by using the in place util.